One persistent trend in the gas turbine industry is the development of smaller, more efficient engines with increased specific power. These changes invariably result in correspondingly higher speed and stress levels on the principal engine components. An engine drive or power shaft is a prime example of this condition since the combination of increased rotor speed and smaller shaft diameter create critical speed problems. One solution is to decrease the effective shaft length by adding additional bearing supports. This creates added mechanical complexities to achieving and assemblying a smaller engine. A simpler and more practical solution to the problem is to construct shafts with higher modules to density ratio which will result in an increased specific stiffness and critical speed.